Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to wireless communication systems for reporting uplink channel feedback.
Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems, and single-carrier frequency division multiple access (SC-FDMA) systems.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. For example, a fifth generation (5G) wireless communications technology (which can be referred to as 5G new radio (5G NR)) is envisaged to expand and support diverse usage scenarios and applications with respect to current mobile network generations. Some technologies utilize time division duplexing (TDD) for communicating using either downlink or uplink communications in a given period of time. In TDD, channel reciprocity can be used to obtain a channel. In channel reciprocity, for example, an access point can obtain a downlink channel via uplink signaling, such as sounding reference signals (SRS). In another example, using channel reciprocity, a user equipment (UE) can obtain an uplink channel via downlink signaling, such as channel state information reference signal (CSI-RS), etc. Moreover, an access point can derive a precoding matrix indicator (PMI) for downlink transmissions based on the uplink signaling (and/or feedback) from the UE and can provide the PMI or a precoder to the UE for performing uplink precoding.
The access point can provide the precoder to the UE by transmitting a precoded downlink CSI-RS. Due to channel estimation error (e.g., based on channel noise), however, the channel measured by the UE in the downlink may be different than the channel estimated by the access point in the uplink. Thus, the uplink precoder derived from the precoded CSI-RS may suffer from the channel estimation noise seen on the downlink and the uplink, and thus may not be effective for precoding transmissions to the access point. For example, singular value decomposition (SVD)-based precoding, which may be used by UEs in precoding transmissions for an access point, may be sensitive to such noise.